Physicists have long suggested that the universe is almost the same in every direction, and have now found a new way to test this hypothesis: by studying the shadow of a black hole.
If this shadow is slightly smaller than existing theories of physics predict, it may help prove a distant idea called bumblebee gravity, which describes what would happen if at first glance the perfect symmetry of the universe is still not so perfect.
If scientists can find a black hole with such an undersized shadow, it will open the door to a whole new understanding of gravity ̵
But to understand how this idea of bees can fly, let’s delve into some basic physics.
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Looking in the mirror
Physicists love symmetry; after all, it helps us understand some of the deepest secrets of the universe. For example, physicists have learned that if you conduct a fundamental physics experiment, you can move your testing equipment elsewhere and get the same result again (ie, if all other factors, such as temperature and gravity, remain the same).
In other words, no matter where in space you conduct your experiment, you will get the same result. By mathematical logic this leads directly to law of conservation of momentum.
Another example: If you start your experiment and wait a while before running it again, you will get the same result (again, other things being equal). This temporal symmetry leads directly to the law of conservation of energy – this energy can never be created or destroyed.
There is another important symmetry that forms the basis of modern physics. It’s called Lorentz Symmetry, in honor of Hendrik Lorenz, the physicist who understood all this in the early 1900s. It turns out that you can do your experiment and rotate it and (other things being equal) you will get the same result. You can also increase your experiment to a fixed speed and still to get the same result.
In other words, all other things being equal – and yes, I repeat this often because it is important – if you run an experiment at complete rest and do the same experiment at half the speed of light, you will get the same result.
This is the symmetry that Lorenz revealed: The laws of physics are the same regardless of position, time, orientation, and speed.
What do we derive from this fundamental symmetry? Well, to begin with, we get the whole special theory of Einstein relativity, which determines a constant speed of light and explains how space and time are related to objects traveling at different speeds.
Gravity of bees
Special relativity is so important to physics that it is almost a metatheory of physics: If you want to come up with your own idea of how the universe works, it must be compatible with the dictates of special relativity.
Or not.
Physicists are constantly trying to come up with new and improved theories of physics, because the old ones, such as the general theory of relativity, which describes how matter deforms space-time and the Standard Model of particle physics, cannot explain everything in the universe. happens in the heart of a black hole. And a very juicy place to look for new physics is to see if a cherished notion might not be as accurate in extreme conditions – valuable notions like Lorentz symmetry.
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Some models of gravity claim that the universe is not exactly symmetrical. These models predict that there are additional ingredients in the universe that force it not to obey Lorentz’s symmetry all the time. In other words, there will be a special or privileged direction in space.
These new models describe a hypothesis called “bee gravity.” It gets its name from the supposed idea that scientists once claimed that bees should not be able to fly because we did not understand how their wings generated lift. (By the way, scientists never really believed that.) We don’t fully understand how these models of gravity work and how they might be compatible with the universe we see, and yet, here they are, looking us in the face as viable. options for new physics.
One of the most powerful applications of bee gravitational models is the potential explanation dark energy —The phenomenon responsible for the observed accelerated expansion of the universe. It turns out that the extent to which our universe breaks the Lorentz symmetry may be related to an effect that generates accelerated expansion. And since we have no idea what dark energy creates, this opportunity seems really attractive.
The black shadow
So, you have a buzzing new theory of gravity based on some crushing icon ideas like breaking symmetry. Where would you go to test this idea? You will go to the place where gravity is stretched to the absolute limit: a black hole. In the new study, which has not yet been reviewed and published online in November 2020 in the preprint database arXiv, researchers did just that, looking at the shadow of a black hole in a hypothetical universe modeled to be as realistic as possible.
(Do not forget that the first of its kind image of a black hole The M87 produced by the Event Horizon telescope just a year ago? This ghostly beautiful, dark void in the center of the bright ring was actually the “shadow” of the black hole, the region that sucked in all the light behind and around it.)
To make the model as realistic as possible, the team placed a black hole in the background of a universe that was accelerating as it expanded (just like what we observe) and adjusted the level of symmetry breaking to match the behavior of the dark energy, which scientists measure.
They found that in this case, the shadow of the black hole could appear up to 10% smaller than in a world with “normal gravity”, providing a clear way to test the gravity of bees. While the current image of the M87 black hole is too blurry to distinguish the difference, efforts are being made to take even better pictures of more black holes, exploring some of the deepest mysteries of the universe in the process.
Originally published in Live Science.
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